The outgoing president also said the UK would become an “outsider” after Brexit, suggesting that the event was “the real end of the British Empire”.
In a speech at the elite College of Europe, Mr Tusk said he envied former Commons speaker John Bercow because he can “finally, honestly say what he thinks about Brexit”.
Citing an anti-totalitarian philosopher Mr Tusk said: “The UK election takes place in one month. Can things still be turned around? Hannah Arendt taught that things become irreversible only when people start to think so.
“So the only words that come to my mind today are simply: Don’t give up. In this match, we had added time, we are already in extra time, perhaps it will even go to penalties?”
The UK’s main opposition parties, including Labour and the Liberal Democrats, have pledged to support a second referendum on EU membership if they can deny Boris Johnson a majority in next month’s election.
Mr Tusk said Brexiteers who believe leaving the European Union will make the UK global again and that “only alone it can truly be great” are wrong.
“The reality is exactly the opposite,” he said. “Only as part of a united Europe can the UK play a global role, only together can we confront, without any complexes, the greatest powers of this world.”
“In fact, I can say the same about Germany or France. And the world knows it. I have heard the same in India, New Zealand, Australia, Canada and South Africa; that after its departure, the UK will become an outsider, a second-rate player, while the main battlefield will be occupied by China, the United States and the European Union.
“’Why are they doing this?’ I was asked this regretful question everywhere I went. One of my English friends is probably right when he says with melancholy that Brexit is the real end of the British Empire.”
Referencing Mr Bercow, who described Brexit as “the biggest foreign policy mistake in the post-war period”, Mr Tusk said: “I want to tell you something I wouldn’t have dared to say a few months ago, as I could be fired for being too frank.
“And today it is simply too late to impeach Donald, at least the European one. In fact, I envy John Bercow, that he can finally, honestly say what he thinks about Brexit.”
Mr Tusk himself has however been outspoken about Brexit before, saying there was a “special place in hell” for those who promoted it during the EU referendum without a plan.
The former Polish prime minister will step down from his post on 1 December handing over to former Belgian prime minister Charles Michel.
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